If Jim missed 6 out of 16 free throws, then he made 10/16 free throws. At the same time Gracia made 4/15 free rows. The common denominator of those fractions (if we simplify 10/16 to 5/8) is 120, so:
Garcia made 4/15 = 32/120 free throws
Jim made 5/8 = 75/120 free throws
We can clearly see that Jim was more than two times better than Garcia